In early paper finishing systems it was generally customary to manually set the speed of each machine so that it produced work pieces at a slightly lower rate than could be handled by the next machine in the line. Thus, a paper finishing system that included a rewinding machine for converting large parent rolls of paper into smaller diameter rolls, or logs, a saw for cutting the logs into lengths used by the consumer, and a wrapper for wrapping the rolls, the log saw speed would be set so that it could cut logs at a faster rate than could be produced by the rewinder, and the wrapper speed would be set so that it could wrap rolls at a faster rate than could be produced by the log saw. When a parent roll has been exhausted the rewinder must be shut down so that a new parent roll can be installed. In such a system, while the rewinder is down for a parent roll change, the flow of logs to the log saw is stopped and the log saw and the wrapper become idle.
It was recognized that the production rate of the finishing system could be increased by incorporating a temporary storage device, called a log accumulator, between the rewinder and the log saw. Such a finishing system is shown and described in U.S. Pat. No. 3,016,780 issued to D. W. Mosen on Jan. 16, 1962. One advantage of having an accumulator is that the rewinder can continue to produce logs even when the log saw is not operating, as the excess logs are stored in the accumulator. Another advantage is that the speed of the rewinder can be set so that it produces logs at a faster rate than can normally be handled by the log saw. If the speed of the rewinder is set properly, when the parent roll is exhausted, there will be a sufficient number of logs stored in the accumulator to allow continued operation of the log saw and wrapper while a new parent roll is placed on the rewinder.
In finishing systems that have an accumulator, there are occasions when the accumulator becomes almost full or full. This could happen, for example, if the saw were shut down for a period of time and the rewinder continued to produce logs. If the rewinder is set to produce logs at a faster rate than can be handled by the log saw, and the accumulator is almost full when the log saw comes back on line, it is possible to jam either the accumulator or the log saw and the rewinder will shut down which usually results in waste. If the rewinder shuts down several times during a relatively short period of time, there is a tendency for the finishing line operator to lower the rewinder speed thereby lowering the probability that the finishing system will ever reach a point where the rewinder can produce more logs than can be instantaneously handled by the accumulator and the log saw. Over the long term, this reduction in speed, although slight, can represent a significant reduction of the average flow rate of product through the finishing system.
It is, therefore, desirable to automatically control the speed of the rewinder to maintain a high flow rate of product through the finishing system. It is also desirable to take into account the status of the rewinder, accumulator and saw when automatically controlling the speed of the rewinder.
It is quite common for a finishing line operator to be responsible for operating two web rewinders. One responsibility of the operator is to replace an exhausted parent roll with a new parent roll. If it should happen that both parent rolls are exhausted at the same time, the first rewinder will be shut down for the time required to change the parent roll, but the second rewinder will be down for the time required to change two parent rolls. Thus, if it appears that both parent rolls will be exhausted at the same time, it would be desirable to automatically control the speed of the rewinders so that the parent rolls will not become exhausted at the same time.